Detector circuit

ABSTRACT

A device comprises a multiplication circuit configured to derive a product of a first signal S 1  and a second signal S 2 , S 2  having a phase difference β relative to the first signal S 1 , a low pass filter configured to remove a selected frequency component from the product of S 1  and S 2  to derive a dot product S 1 ·S 2 ; and a calculation circuit configured to receive the dot product S 1 ·S 2  and generate a signal output having a ratio |S 1 |/|S 2 | and the phase difference β.

BACKGROUND

1. Field

The present invention relates to detector circuits, e.g. for impedance measurement systems.

2. Background

Impedance measurement systems can be used to determine the impedance of a signal path in a mobile communication device where the signal path's impedance depends on its external conditions. In other words, where the signal path has a variable load impedance. In the case of mobile communication devices with an antenna, the variable load impedance can be due to the antenna's changing environment.

In order to optimize the transmission coefficient of transmit (Tx) or receive (Rx) signals propagating in the signal path, the signal path's actual impedance must be known.

Conventional impedance measurement systems use two receive signal strength indicator (RSSI) chains as level detectors to measure two signal levels. An additional phase detector is needed to measure the phase between the two signal levels.

It would be desirable to provide a detector circuit for an impedance measurement system, without the need for an additional phase detector and without the need for a level detector, e.g. an RSSI-chain.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures, like reference numerals refer to like parts throughout the various views unless otherwise indicated. For reference numerals with letter character designations such as “102 a” or “102 b”, the letter character designations may differentiate two like parts or elements present in the same figure. Letter character designations for reference numerals may be omitted when it is intended that a reference numeral encompass all parts having the same reference numeral in all figures.

FIG. 1 schematically shows a detector circuit DC comprising a multiplication circuit MC and a calculation circuit CC.

FIG. 2 shows an equivalent circuit diagram of a signal path comprising an unknown load impedance Zx and a sensing impedance Zsense.

FIG. 3 shows fundamental correlations between the different input signals and their respective phase differences.

FIG. 4A schematically shows a detector circuit comprising a multiplication circuit MC, a low pass filter LPF, a calculation circuit CC, and an analog/digital converter ADC.

FIG. 4B shows an embodiment of a detector circuit where an analog/digital converter is connected between a low pass filter LPF and a calculation circuit CC.

FIG. 4C shows an embodiment of a detector circuit with three signal inputs.

FIG. 5 shows a detector circuit DC comprising three subtraction circuits, three multiplication circuits, three low pass filters, three analog/digital converters ADC and a calculation circuit CC.

FIG. 6 shows an embodiment of a detector circuit similar to that of FIG. 5, further comprising amplifiers AMP.

FIG. 7 shows an embodiment of the multiplication circuit comprising two Gilbert cells GC.

FIG. 8 is a flowchart showing an exemplary embodiment of a method for operating a detector circuit.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects.

In this description, the term “application” may also include files having executable content, such as: object code, scripts, byte code, markup language files, and patches. In addition, an “application” referred to herein, may also include files that are not executable in nature, such as documents that may need to be opened or other data files that need to be accessed.

The term “content” may also include files having executable content, such as: object code, scripts, byte code, markup language files, and patches. In addition, “content” referred to herein, may also include files that are not executable in nature, such as documents that may need to be opened or other data files that need to be accessed.

An exemplary embodiment of a detector circuit comprises a first signal input determined to receive a first signal S₁, a second signal input determined to receive a second signal S₂ having a phase difference β relative to the first signal S₁, and a multiplication circuit determined to derive the dot product S₁·S₂. Further, the detector circuit comprises a signal output determined to provide the ratio |S₁|/|S₂|. The signals S₁ and S₂ can be visualized in the complex plane and, thus, be interpreted as vectors. Accordingly the dot product S₁·S₂ is a well-defined quantity.

An exemplary embodiment of a detector circuit may be used in an impedance measurement system for a signal path shown in FIG. 2. The signal path SP may be connected to an antenna having a variable load impedance. Such an antenna and its load impedance is represented by an impedance Z_(x). Further, the signal path SP comprises a sensing impedance Z_(sense) which may be an inductive element IE. V₂₀ denotes the voltage drop of the load impedance Z_(x). V₁₂ denotes the voltage drop across the impedance Z_(sense). V₁₀ is the sum of the voltages V₂₀ and V₁₂: V₁₀=V₂₀+V₁₂. Thus, the impedance of the signal path SP equals the load impedance Z_(x) plus the sensing impedance Z_(sense) which may be a known impedance. From FIG. 2, it is clear that Z=Z_(sense) V₁₀/V₁₂ where V₁₀ and V₁₂ are voltages representable as complex numbers.

The situation shown in FIG. 2 can be described with parameters other than voltages V₁₀, V₁₂, and V₂₀, i.e. exemplary embodiments of the detector circuit do not depend on details of parameters used as signal inputs for the detector circuit. Other parameters, e.g. current information, are also possible.

Thus, deriving the unknown impedance Z can be accomplished by determining the ratio V₁₀/V₁₂. Here, V₁₀ may be written as V₁₀=|V₁₀| exp (jωt). Then, V₁₂ may be written as V₁₂=|V₁₂|exp ((jωt)+φ), i.e. V₁₀ and V₁₂ are signals of the same frequency with a phase difference of φ between V₁₀ and V₁₂. Accordingly, the ratio V₁₀/V₁₂ can be written as V₁₀/V₁₂=|V₁₀|/|V₁₂| exp (jφ). The correlations between V₁₀, V₁₂, and V₂₀ are drawn in a complex plane view in FIG. 3.

Accordingly, deriving the ratio V₁₀/V₁₂ can be accomplished by deriving the ratio of the absolute values |V₁₀|/|V₁₂| and by obtaining a measure for the phase difference φ. Previous circuits use two RSSI-chains to obtain the ratio of the absolute values. A further discrete phase detector is then used to obtain phase information.

Exemplary embodiments of the detector circuit are based on the fact that the complex ratio V₁₀/V₁₂ intrinsically comprises the phase information. In an exemplary embodiment, the detector circuit provides direct access to phase information by processing three signals, e.g. V₁₀, V₂₀ and V₁₂.

In an exemplary embodiment, the detector circuit uses a geometric correlation between signal levels and phase information and electric circuitry that makes use of this correlation.

Accordingly, an exemplary embodiment of the detector circuit comprises a multiplication circuit that derives the dot product V₁₀·V₁₂ when V₁₀ equals S₁ and V₁₂ equals S₂.

V₁₀·V₁₂=|V₁₀∥V₁₂| cos φ. Thus, the dot product V₁₀·V₁₂ is proportional to cos φ as a measure for the phase difference φ.

In an exemplary embodiment, the detector circuit further comprises a third signal input configured to receive a third signal S₃ having a phase difference α relative to the first signal S₁.

Since S₁−S₂=S₃, two signals, selected from S₁, S₂ and S₃ already contain enough information to determine the complex impedance Z. Processing the third signal enables technically advanced exemplary embodiments of the detector circuit with higher accuracy.

In an exemplary embodiment, the multiplication circuit derives three dot products S₁·S₂, S₂·S₃, and S₁·S₃.

When the dot products S₁·S₂, S₂·S₃, and/or S₁·S₃ are known then all ratios |S₁|/|S₂|, |S₁|/|S₃|, |S₃|/|S₂| and the respective inverse ratios can be obtained. Further, the values for cos α, cos β, and cos γ as measures for the phase differences between the signal inputs (α being the phase difference between S₁ and S₃; β being the phase difference between S₁ and S₂, γ being the phase difference between S₂ and S₃) can be obtained.

In an exemplary embodiment, one of the signals S₁, S₂, S₃ is the sum of the respective other two signals.

In an exemplary embodiment the multiplication circuit comprises a multiplier and a low pass filter.

The multiplier circuit of the multiplication circuit may be fed with input signals of the form:

V ₁(t)=|V ₁|sin ωt  (1)

V ₂(t)=|V ₂|sin(ωt+φ′)  (2)

Multiplication yields:

V ₁(t)V ₂(t)=½|V ₁ ∥V ₂|{cos φ′−cos(2ωt+φ′)}  (3)

The low pass filter may absorb the component of the frequency 2ω and provide a signal proportional to |V₁∥V₂| cos φ′, which is exactly the dot product of V₁·V₂.

Thus, with V₁, V₂ being two values selected from S₁, S₂, S₃, each of the dot products S₁·S₂, S₂·S₃, and S₁·S₃ can be obtained.

With:

k ₁ =S ₁ ·S ₂ /S ₂ S ₃

k ₂ =S ₁ ·S ₂ /S ₁ ·S ₃

k ₃ =S ₂ ·S ₃ /S ₁ ·S ₃

The ratios of the rational numbers |S₁|/|S₂| can be obtained:

(|S ₁ |/|S ₂|)² =k ₁(k ₂+1)/(k ₂(k ₁−1))

and

|S ₁ |/|S ₂|=√{square root over (k1(k2+1)/(k2(k1−1)))}{square root over (k1(k2+1)/(k2(k1−1)))}

Similarly |S₁|/|S₃| and |S₂|/|S₃| can be obtained.

Further, by utilizing the cosine rule c²=a²+b²−2ab cos γ (with γ being the phase difference between a and b and a, b and c being understandable as the sides of a triangle) measures for the phase differences between the input signals can be obtained:

cos β=½(|S ₁ |/|S ₂ |+|S ₂ |/|S ₁|−(|S ₃ |/|S ₁ ∥S ₃ |/|S ₂|)).

Similarly the respective other two phase differences can be obtained.

Thus, obtaining all three input signals S₁, S₂, S₃ is preferred. However, exemplary embodiments of the detector circuit can also work with two inputs for signals S₁, S₂ only. This is if the detector works in a mode where the three different signals are provided one after another. Then, a memory is used for storing processed values, but only one calculation circuit is needed.

In an exemplary embodiment, the first signal S₁, the second signal S₂ and the third signal S₃ are voltage or current signals. Then, S₁ can equal V₁₀, S₂ can equal V₁₂ and S₃ can equal V₂₀. The phase difference between V₁₀, V₁₂ and V₂₀ are φ, ψ and χ as shown in FIG. 3.

In an exemplary embodiment, the detector circuit further comprises a calculation circuit. The calculation circuit can obtain signals that are proportional to |V₁∥V₂| cos φ′ for V₁ and V₂, etc. being the input signals from the multiplication circuit. Based on the above equations the ratios |S₁|/|S₂|, |S₁|/|S₃|, |S₂|/|S₃| and measures for the phase differences β, α, and γ=180°−β−α can easily be derived via the calculation circuit.

In an exemplary embodiment, the detector circuit further comprises an analog/digital converter. The analog/digital converter can be connected between the multiplication circuit and the calculation circuit. Then the calculation circuit works in the digital domain. However, it is possible that the calculation circuit works in the analog domain and the analog/digital converter is connected behind the calculation circuit.

In an exemplary embodiment, the analog/digital converter is connected before the multiplication circuit. Then, the multiplication circuit and the calculation circuit can work in the digital domain. In this configuration, the multiplication circuit can be integrated in the calculation circuit.

In an exemplary embodiment, the detector circuit further comprises two subtraction circuits determined to derive V₁₀ and V₁₂ from three input potentials P₀, P₁, P₂.

In an exemplary embodiment, the detector circuit further comprises a feedback network that generates information about the ratio of two dot products.

In an exemplary embodiment, the multiplication circuit of the detector circuit comprises two (2) double balanced mixers or Gilbert cells, a circuit that is adapted to iteratively generate a digital code based on up/down information at an 1 bit input or an updown-counter, and a feedback network.

In an exemplary embodiment, the signal output of the detector circuit is determined to provide the ratios |V₁₀|/|V₁₂|, |V₁₂|/|V₂₀|, |V₂₀|/|V₁₀|, a measure for the phase difference φ between V₁₂ and V₁₀, a measure for the phase difference ψ between V₂₀ and V₁₀, and a measure for the phase difference χ between V₂₀ and V₁₂.

In an exemplary embodiment, the detector circuit is an impedance detector that may be utilized in an impedance measurement system, e.g. of a mobile communication device.

In an exemplary embodiment, the calculation circuit of the detector circuit utilizes a lookup table. A lookup table is a simple but effective means to obtain an angle α from cos α. Thus, the phase differences φ, ψ, and χ can easily be provided at the signal output of the detector circuit.

FIG. 1 schematically shows an embodiment of the detector circuit DC 100 comprising a multiplication circuit MC 110 provided for obtaining two input signals S₁, S₂ at at least two signal inputs (SI₁, SI₂). The two signals S₁ and S₂ may have a form as shown in equations 1 and 2. By multiplying these two signals, e.g. via a dot product circuit in the multiplication circuit MC 110, a product signal is obtained that contains different frequency components as shown in equation 3. The frequency component having a frequency of 2ω is removed by the low pass filter LPF 120 connected after the multiplication circuit MC 110. As a result, the low pass filter LPF 120 provides an output signal that is mainly proportional to the dot product S₁·S₂. This dot product is analyzed by the calculation circuit CC 130. The dot product S₁·S₂ contains information about the absolute value of S₁, the absolute value of S₂ and the phase difference between S₁ and S₂. By extracting the respective information from the input signals, the detector circuit DC 100 is able to provide the ratios. The input signals S1, S2 can carry three different quantities such as electric potentials, voltages or currents simultaneously or one after another.

A multiplication circuit can comprise conventional mixer circuits and further circuit components. The multiplication circuit is, thus, not restricted to a mixer circuit.

FIG. 2 schematically shows a signal path SP 210 in which radio frequency signals may propagate. A potentially variable load impedance is denoted as Z_(x) 212. Further, the signal path SP 210 comprises a sensing element Z_(sense) 220 used for determining impedance information Z_(x). The sensing impedance Z_(sense) 220 could be established by an inductive element IE. V₁₀, V₂₀, and V₁₂ could be the voltage differences, between the potentials P₀, P₁, and P₂ respectively. In the circuit shown in FIG. 2, when the signals V₁₀, V₁₂, and V₂₀ are voltages, then V₁₀=V₁₂+V₂₀.

FIG. 3 shows the correlations between the input signals V₁₂, V₁₀, and V₂₀. V₁₂ could be the voltage drop across the sensing element Z_(sense), which may be an inductive element. V₁₀ may be the voltage between the input of the signal path and a ground potential. V₂₀ is the voltage drop across the unknown load impedance Z_(x). Then, V₁₀ is the sum of voltages V₁₂ and V₂₀. Accordingly, the three voltages establish a triangle defined by the length of the vectors and the respective angles. The cosine of each angle is determined by the ratios of the side lengths of the triangle.

FIG. 4A shows an embodiment of the detector circuit 400 where an analog/digital converter ADC 450 is connected after the calculation circuit CC 430. Then, it is possible that a multiplier of the multiplication circuit MC 410, the low pass filter LPF 420 and the calculation circuit CC 430 work in the analog domain. The analog/digital converter ADC 450 provides digital information about amplitudes, amplitude ratios, and/or phase differences.

FIG. 4B shows an embodiment of the detector circuit 401 where the analog/digital converter ADC 450 is connected between the low pass filter LPF 420 and the calculation circuit CC 430. Then, it is possible that a multiplier of the multiplication circuit MC 410 and the low pass filter LPF 420 work in the analog domain while the calculation circuit CC 430 works in the digital domain. It is, however, possible that the input signals, e.g. V₁₀ and V₁₂, are directly fed into an analog/digital converter ADC 450 and multiplication, low pass filtering and the calculation of amplitude information or phase difference information is done in the digital domain.

FIG. 4C shows an embodiment of the detector circuit 402 where three input signals S₁, S₂, S₃ can be received via signal inputs SI₁, SI₂, SI₃ and processed simultaneously. Otherwise, the information may be provided by signals applied to two inputs one after another.

FIG. 5 shows an embodiment of the detector circuit DC 500 where input signals V₁₀, V₁₂, and V₂₀ are generated as voltage differences between electrical potentials P₁, P₀, and P₂. The detector circuit DC 500 comprises subtractors 505 a, 505 b and 505 c, configured to generate voltage differences between electrical potentials P₁, P₀, and P₂. The detector circuit DC 500 comprises three chains, each chain comprising a multiplier 510 a, 510 b, 510 c, a low pass filter LPF 520 a, 520 b, 520 c, and an analog/digital circuit ADC 550 a, 550 b, 550 c. With such a three-chain solution, the three dot products can be retrieved simultaneously which can be used to calculate phase differences and level ratios. The multiplication circuit MC comprises at least three sections. Each subsection may comprise a mixer and further circuit components.

FIG. 6 shows an embodiment of the detector circuit 600 where the dot product ratios k₁ and k₂ can be obtained by a feedback loop. The detector circuit DC 600 comprises subtractors 605 a, 605 b and 605 c, configured to generate voltage differences between electrical potentials P₁, P₀, and P₂. The detector circuit 600 comprises three chains. Each chain comprises a multiplier 610 a, 610 b, 610 c, a low pass filter, LPF, 620 a, 620 b, 620 c, an amplifier, AMP, 622 a, 622 b, 622 c, e.g. a variable gain amplifier and optionally an additional low pass filter, LPF, 625 a, 625 b, 625 c. The second chain and the third chain have a feedback loop between the second low pass filter 625 b, 625 c, and the respective amplifier, AMP, 622 b, 622 c. The amplifiers 622 b, 622 c can be variable gain amplifiers. The feedback loop comprises an additional operational amplifier OA 660 b and 660 c in the second and third chains. The dot products are obtained at the output of the first low pass filter LPF 620 a, 620 b, 620 c of each chain. The feedback loop ensures that the multiplied dot products are identical. For that, the output of the second low pass filter LPF 625 a of the first chain is connected to the operational amplifiers OA 660 b and 660 c of the second and third chain, respectively. As a result of the feedback loops 665 b, 665 c of the second and third chain, respectively, connected to the output of the second low pass filter 625 a of the first chain, the ratio of the gain of the second amplifier 622 b and the gain of the first amplifier 622 a is identical to the ratio of the dot products: (V₁₀·V₁₂)/(V₂₀·V₁₂). The ratio of the gain of the third amplifier 622 c and the first amplifier 622 a is identical to the ratio of the dot products: (V₁₀·V₁₂)/(V₁₂·V₂₀). When the gain of the first amplifier 622 a is A₀, the gain of the second amplifier 622 b is A₁ and the gain of the third amplifier 622 c is A₂ then k₁=A₂/A₀ and k₂=A₁/A₀. If A₀ is a known fixed value A₁ and A₂ can be the input of analog/digital converters ADC 650 a, 650 b from which k₁ and k₂ can be derived by the calculation circuit CC 630.

FIG. 7 shows an equivalent circuit diagram of a section of a detector circuit comprising two double balanced mixers, i.e. Gilbert cells GC 710 and 720. The lower double balanced mixer 720 multiplies V₁₂ and V₁₀. The upper double balanced mixer 710 multiplies V₂₀ and V₁₀. The outputs are subtracted from each other by combining the collectors and low pass filtering by the capacitor CAP 715. The differential output voltage is the difference of the two amplified dot products. A comparator COMP 760 in a feedback network FN 765 connected to the combined output of these multiplication circuits, i.e. mixers 710, 720, controls the up/down port of an up/down counter UDC 770 and the contents of the up/down counter UDC 770 controls one of the mixer gains by controlling its tail current. When settled, the ratio of the two tail currents is the ratio of the two dot products and is expressed directly in the digital contents of the up/down counter UDC 770. Instead of the up/down counter UDC 770, another digital block that, e.g. iteratively, generates a digital word based on the comparator output is also possible. Such a block may be a SAR-block (SAR=Successive Approximation Register).

Another system can be used to obtain a dot product ratio, e.g. k₁, as a digital word. Then, k₁ and k₂ can be used directly for the required calculations.

FIG. 8 is a flowchart showing an exemplary embodiment of a method for operating a detector circuit. In block 802, three dot products are determined using at least two input signals. In block 804, at least two dot product ratios are generated from the three dot products. In block 806, amplitude ratios and phase differences are derived for the at least two input signals using the at least two dot product ratios.

The detector circuit is not limited to the embodiments described in the specification or shown in the figures. Phase detectors comprising further elements such as further multiplication circuits, filter circuits and/or calculation circuits or combinations thereof are also comprised by the present invention. The features shown above do not exclude each other. The phase detector can comprise each feature in combination with other features.

LIST OF REFERENCE SYMBOLS

-   ADC: analog/digital circuit; -   CAP: capacitive element; -   CC: calculation circuit; -   COMP: comparator; -   DC: detector circuit; -   FN: feedback network; -   GC: Gilbert cell; -   IE: inductive element; -   LPF: low pass filter; -   MC: multiplication circuit; -   OA: operational amplifier; -   P₁, P₀, P₂: electric potentials; -   S₁, S₂, S₃: input signals; -   SI₁, SI₂, SI₃: signal inputs; -   SO: signal output; -   SP: signal path; -   SU: subtraction circuit; -   UDC: up/down counter; -   V₁₀, V₁₂, V₂₀: input signals; -   V₁, V₂: input signals; -   Z, Z_(sense), Z_(x): impedances; -   α, β, γ: phase differences between input signals; -   φ′, φ, χ, ψ: phase differences between input voltages or currents.

The detector circuit described herein may be implemented on one or more ICs, analog ICs, RFICs, mixed-signal ICs, ASICs, printed circuit boards (PCBs), electronic devices, etc. The detector circuit may also be fabricated with various IC process technologies such as complementary metal oxide semiconductor (CMOS), N-channel MOS (NMOS), P-channel MOS (PMOS), bipolar junction transistor (BJT), bipolar-CMOS (BiCMOS), silicon germanium (SiGe), gallium arsenide (GaAs), heterojunction bipolar transistors (HBTs), high electron mobility transistors (HEMTs), silicon-on-insulator (SOI), etc.

An apparatus implementing the detector circuit described herein may be a stand-alone device or may be part of a larger device. A device may be (i) a stand-alone IC, (ii) a set of one or more ICs that may include memory ICs for storing data and/or instructions, (iii) an RFIC such as an RF receiver (RFR) or an RF transmitter/receiver (RTR), (iv) an ASIC such as a mobile station modem (MSM), (v) a module that may be embedded within other devices, (vi) a receiver, cellular phone, wireless device, handset, or mobile unit, (vii) etc.

In one or more exemplary designs, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

As used in this description, the terms “component,” “database,” “module,” “system,” and the like are intended to refer to a computer-related entity, either hardware, firmware, a combination of hardware and software, software, or software in execution. For example, a component may be, but is not limited to being, a process running on a processor, a processor, an object, an executable, a thread of execution, a program, and/or a computer. By way of illustration, both an application running on a computing device and the computing device may be a component. One or more components may reside within a process and/or thread of execution, and a component may be localized on one computer and/or distributed between two or more computers. In addition, these components may execute from various computer readable media having various data structures stored thereon. The components may communicate by way of local and/or remote processes such as in accordance with a signal having one or more data packets (e.g., data from one component interacting with another component in a local system, distributed system, and/or across a network such as the Internet with other systems by way of the signal).

Although selected aspects have been illustrated and described in detail, it will be understood that various substitutions and alterations may be made therein without departing from the spirit and scope of the present invention, as defined by the following claims. 

What is claimed is:
 1. A device, comprising: a multiplication circuit configured to derive a product of a first signal S₁ and a second signal S₂, S₂ having a phase difference β relative to the first signal S₁; a low pass filter configured to remove a selected frequency component from the product of S₁ and S₂ to derive a dot product S₁·S₂; and a calculation circuit configured to receive the dot product S₁·S₂ and generate a signal output having a ratio |S₁|/|S₂| and the phase difference β.
 2. The device of claim 1, further comprising a third signal input configured to receive a third signal S₃ having a phase difference α relative to the first signal S₁.
 3. The device of claim 2, wherein: the first signal S₁ is a voltage V₁₀ across a serial connection of a sensing impedance Z_(sense) and a further impedance Z_(x); the second signal S₂ is a voltage V₁₂ across the sensing impedance Z_(sense); and the third signal S₃ is a voltage V₂₀ across the further impedance Z_(x).
 4. The device of claim 2, wherein the multiplication circuit and the low pass filter are configured to derive three dot-products S₁·S₂, S₂·S₃, and S₁·S₃.
 5. The device of claim 2, wherein one of the signals S₁, S₂, S₃ is the sum of the respective other two signals.
 6. The device of claim 2, wherein the first signal S₁, the second signal S₂ and third signal S₃ are selected from voltage signals or current signals.
 7. The device of claim 3, further comprising three subtraction circuits configured to derive V₁₀ and V₁₂ from three input potentials P₀, P₁, P₂.
 8. The device of claim 4, further comprising a feedback network configured to generate information about the ratio of two of the dot products S₁·S₂, S₂·S₃, and S·S₃.
 9. The device of claim 1, wherein the multiplication circuit further comprises: two (2) double balanced mixers or Gilbert cells and a capacitance configured to generate a differential output voltage that represents the difference of two amplified dot products; a comparator configured to receive the differential output voltage and generate an up/down signal; and an up-down-counter responsive to the up/down signal and configured to control at least one of the two (2) double balanced mixers or Gilbert cells.
 10. The device of claim 3, wherein the signal output is configured to provide: the ratios |V₁₀|/|V₁₂|, |V₁₂|/|V₂₀|, |V₂₀|/|V₁₀|; a measure for the phase difference φ between V₁₂ and V₁₀; a measure for the phase difference ψ between V₂₀ and V₁₀; and a measure for the phase difference γ between V₂₀ and V₁₂.
 11. The device of claim 1, wherein the device is an impedance detector.
 12. A method comprising: determining three dot products using at least two input signals; generating at least two dot product ratios from the three dot products; and deriving amplitude ratios and phase differences between any set of two of the at least two input signals using the at least two dot product ratios.
 13. The method of claim 12, further comprising using the amplitude ratios and phase differences of the at least two input signals to determine an impedance in an impedance measurement system.
 14. A device, comprising: means for determining three dot products using at least two input signals; means for generating at least two dot product ratios from the three dot products; and means for deriving amplitude ratios and phase differences of the at least two input signals using the at least two dot product ratios.
 15. The device of claim 14, further comprising means for determining an impedance in an impedance measurement system. 